It has long been desirable to provide a carpeting material which suitably dissipates build up of static electricity without being positively grounded. The need for effective static dissipation is particularly urgent in computer rooms and the like. Heretofore, carpetings have been provided which contained metallic threads and other such means to diminish static electricity. Also, positive grounding of such carpets with wires and nails has been effective, albeit inconvenient in many circumstances.
However, there is no art known which suggests the particular combination of constructions to be disclosed below, particularly in view of their extraordinary ability to dissipate static electricity without causing discomfort to pedestrians who have walked off, or who are walking upon the carpet.
In a hindsight evaluation of the invention, it may be said that it is a unique extension and combination of elements relating to all of the following areas of generally recognized art:
(1) carpets comprising conductor elements; PA1 (2) sheets containing conductive fillers; and PA1 (3) mats comprising foam and plastic backing. PA1 (1) A conductive tufting yarn, of the type described in U.S. Pat. No. 3,723,811. A nylon yarn of this type is commercially available form Dow Badische Company of Williamsburg, Va., under the trade designation Y-514S and is wholly suitable for use in the products of the invention. In the product of the invention, it is suitable to utilize a product having less than 1%, indeed as low as 0.2%, by weight of conductive fiber. One conductive fiber advantageously used is that of the type sold by Dow Badische Company under the trade designation F-901. This is a nylon-type of yarn impregnated or coated with conductive carbon. It is more break-resistant that metal yarns of the prior art and, consequently, the electroconductivity thereof is more durable in the products of the invention. PA1 (i) a vinyl based material and PA1 (ii) a polymeric foam, advantageously a low density urethane reticulated foam forming the floor-contacting side of the backing and of the rug. The backing is conveniently of the type generally described in U.S. Pat. No. 3,804,699, i.e. of the type previously used in mats to achieve a creep-resistant property. Usually the foam is largely impregnated by the polymer-based composition, but a distinct non-impregnated portion of foam forms the bottom of the backing. PA1 (1) will provide a means to reduce the static level to 3,000 volts or less from, typically, 7,000 to 12,000 static volts, immediately upon a "charged" person stepping onto the mat; or PA1 (2) will minimize the voltage build up by a person walking on the carpeting material.